This disclosure is directed to sensor tags and more particularly chipless and wireless sensor circuits.
Sensor tags use RF backscattering systems to enabling wireless charging to eliminate the need for batteries. Wireless sensor tags are advantageous for many wearable and implantable applications, such as for healthcare and structural health/safety monitoring of structures, for example, buildings and bridges. However, prior art sensor tags and sensor tag circuits require a CMOS chip for performing functions such as voltage regulation/bandgap reference, analog-to-digital conversion, current (or voltage) to frequency conversion, pulse generation and frequency modulation. The CMOS chip consumes area, adds weight, reduces mechanical flexibility and increases cost. Even though thin-film transistors capable of operating at RF are available (e.g., low-temperature poly-Si or oxide devices which are much simpler and cheaper than CMOS and compatible with flexible substrates), the CMOS circuits are too complicated to be implemented with non-complementary and lower performance thin-film transistors.